The discovery of the utility of the compounds of formula (I) in the field of perfumery and flavours is particularly surprising. In their pure state in fact, these compounds develop a very powerful and unpleasant smell and it is only upon dilution that their odoriferous and flavouring properties become apparent.
The compounds of formula (I) belong to the class of derivatives known as 1,3-oxathianes (n=1) and 1,3-oxathiolanes (n=0). Their use, as well as that of their corresponding oxides (m=1), was hitherto unknown in perfumery and in the flavour art.
We have discovered 2-methyl-4-n-propyl-1,3-oxathiane and its corresponding oxide, viz. 2-methyl-4-n-propyl-1,3-oxathiane-3-oxide, as compounds of natural origin which can be isolated from an essential oil obtainable from the juice of the passion-fruit, Passiflora edulis flavicarpa. Passion-fruit juice is a commercial material available, for example, from Nationwide of Chicago, Food Brokers, Inc., 1400 Winston Plaza, Melrose Park, Ill., United States.
However, the procedure for isolating the said compounds from natural passion-fruit juice is extremely complex and uneconomical. The yield of essential oil obtained is not higher than 0.0012% by weight of the total juice treated. In order to isolate the above mentioned compounds, the juice is subjected to a preliminary distillation, by means of a special technique known as "thin layer distillation"--vide Helv. Chim. Acta, 45, 2186 (1962). This operation yield 18% by weight of an aqueous distillate from which the desired essential oil can be obtained by extraction with ethyl chloride followed by evaporation of the volatile components. The oil is then separated by column chromatography on silicic acid, by the procedure described in J. Chromatography 34, 174 (1968); and the polar fractions are then subjected to repeated separations by preparative gas chromatography to isolate the pure oxathiane derivatives.
Analytical and synthetic studies confirmed that these products were compounds of previously unknown structure.
The disadvantages and difficulties inherent in the isolation of 2-methyl-4-n-propyl-1,3-oxathiane and 2-methyl-4-n-propyl-1,3-oxathiane-3-oxide from the essential oil obtained from passion-fruit have been overcome by the discovery of a process for synthetically preparing these and the other compounds of formula (I). A particularly valuable feature of the synthetic process is that it readily yields the pure compounds, which have powerful organoleptic characteristics that are stable and perfectly reproducible; whereas, in contradistinction, the properties of the natural essential oil vary with the origin of the fruit from which it has been extracted, the method of extraction, and the purity of the essential oil recovered. Consequently, the synthetic compounds are useful as flavouring and perfuming ingredients over a wider field of application than the natural essential oil.
2-Isopropyl-1,3-oxathiolane and its phenyl analogue have been described by Kipnis et al. J.Am.Chem.Soc., 71, 3555 (1949) as liquids with fresh, aromatic aromas. In actual experience the compounds of the invention possess organoleptic properties which are by far, more superior than those described by Kipnis. The following Tables show the results of flavour evaluations carried out on 2-methyl-4-propyl-1,3-oxathiane in comparison with 2-isopropyl-1,3-oxathiolane and 2-phenyl-1,3-oxathiolane.
______________________________________ Evaluation in water Ingredient Level Evaluation ______________________________________ 1. 2-Methyl-4- 0.1 ppm Sweet, green, fruity propyl-1,3- typical Passion-fruit oxathiane (100%) ##STR2## 0.10 ppm Strong alliaceous note, Cabbage, gas, burnt. Rotten egg. ##STR3## 0.20 ppm Weaker than 1, less fruity. Woody, floral. Slight egg character ______________________________________
______________________________________ Evaluation in acidified sugar syrup* Ingredient Level Evaluation ______________________________________ 1. 2-Methyl-4- 0.10 ppm Fruity, juicy. propyl-1,3- Typical Passion-fruit. oxathiane Blackcurrant. (100%) ##STR4## 0.10 ppm Lacks fruit juicy cha- racter. Burnt, gas top note. Alliaceous. ##STR5## 0.20 ppm Less fruity than 1. Woody, floral. Vegetable character. ______________________________________ *10 g of a 50% aqueous solution of citric acid in a syrup containing 600 of sucrose per liter water.
______________________________________ As reinforcer for natural Passion-fruit Juice - Comparison made with unflavoured juice. Ingredient Level Evaluation ______________________________________ 1. 2-Methyl-4- 0.10 ppm Enhanced juicy character. propyl-1,3- Fresher top note. oxathiane Typical. (100%) ##STR6## 0.10 ppm Burnt, alliaceous, Coffee. Not recognizable. Direction Durian. ##STR7## 0.20 ppm Green vegetable character. Cooked, fatty. Not typical. ______________________________________
Concerning its olfactive properties, 2-methyl-4-propyl-1,3-oxathiane is clearly distinguishable from the above cited oxathiolane derivatives described by Kipnis. 2-Isopropyl-1,3-oxathiolane possesses an extremely powerful almost unbearable smell in its pure state. Upon dilution the same compound developed a strong odour reminiscent of rotten grass and sewage with a "carbide" by-note. 2-Phenyl-1,3-oxathiolane showed a slight spicy-green character and a vague odour reminiscent of bitter almonds with a slight rotten smell. On the contrary, 2-methyl-4-propyl-1,3-oxathiane develops in a 1% by weight solution in diethyl-phthalate a pleasant scent having a fruity-green and fresh character reminiscent of the odour developed by blackcurrent shrub leaves.
Several oxathiane and oxathiolane derivatives have been reported in the past in the scientific literature. 2-(3-Heptyl)-1,3-oxathiolane and 2-(3-amyl)-1,3-oxathiolane have been described in U.S. Pat. No. 3,025,214. Pasto et al. [J.Am.Chem.Soc., 89, 4368 (1967)] have prepared various 1,3-oxathianes which may be alkylated in the 2-position. Van Acker et al. [Tetrahedron Letters 1974, 225-8] and Stevenson [J.Am.Chem.Soc., 96, 1067 (1974)] have described 1,3-oxathiane-5-oxides and 2-t-butyl-1,3-oxathiolanes, respectively. Djerassi et al. [J.Am.Chem.Soc., 75, 3704 (1953)], Rondestvedt [J. Org. Chem. 26, 2247 (1961)], De Wolf et al. [Tetrahedron Letters, 1970 551-4], Pihlaja et al. [Acta Chem. Scand. 1970, [24], 2257] and Pasanen et al. [Acta Chem. Scand. 1971, [25] 1908] showed a variety of 1,3-oxathianes which may be substituted in the 2-and the 6-positions.
None of the above cited references describes or even suggests the possibility of using the oxathiane or oxathiolane derivatives of the present invention as flavour or perfume ingredients and, what is more, no mention appears therein of the organoleptic properties of the described compounds, most of the cited authors having in fact limited their investigations to pure theoretical physicochemical studies.